I had no idea before but just discovered there is a fifth bulb, closest to the license plate, that seems to be a spare in each of the tail light housings. (81 300SD).
Does not seem to have any contacts to make them operable.

The two rear inner lights are rear fog lights, we'll actually just the left side is a true fog light i think, the other side is there for asthetics. Rear fogs weren't legal for you guys (americans) the time your vehicle was built and thus there not wired.

Not true (re legality). Some (but not all) MB's in the USA prior to 1985 had rear fogs -- it was dropped as a USA feature then, and wasn't reintroduced in any models until 1991 (when it became standard in all models here in the USA). However, in 1986, all USA Volvos and some other luxury makes (e.g., Jaguars) started included them.
MB also only uses a rear fog on the left side -- most other makes use a pair of them.
If you have that bulb in that socket, you've probably got the feature (because you have the electrical contacts necessary to keep the bulb securely in place -- cars without also lack the metal contacts in the socket).
To see if you have the feature, turn your lights on and pull the switch out to the *SECOND* detent (the first detent only operates the front fog lights; the second turns on both front and also rears). When you turn on your rear fogs, if they work the little yellow window in the middle of the light switch should also light up -- it's a required indicator to remind you that your rear fogs are on.
Let us know what happened.
Regards,
Ken

No wires going to the left rear fog bulb opening....nor is there a socket itself.
Just bare metal hole to accomodate a socket.
I found a new bulb that was loose rolling around inside the left fog lens, which led me to believe it was a spare after not finding any sort of electrical wire or contacts.
Anyway, the same story for the right side.
After fishing out the bulb I tried to plug it back in the hole but it doesn't hold well, which leads me to believe the previous owner thought it would be a good place to keep a spare and not MB's original intention.
By the way, this is a 81 300SD.
I don't think it was legal in 81.
My '85 volvo wagon has rear red fog lights on both sides and is kindof obnoxious if there isn't bad weather to cut down on the intensity, so it works when appropriate.
But back to the Benz talk...

moraine/terry;
yes, you can wire up the empty sockets in your car. I have worked for 10+ years with a MB tech who has 30 years exp. and he wired up his 280E so that he had 4 brake lamps. Since there was no 'third' brake lamp this really would get the attention of the person behind you (him). Feel free to do it if you really want to!

I'm wondering if I might be able to get rear foglights working on my 300CDs. Perhaps somehow I could acquire two electrical connectors for the empty sockets there now and run new wire (?) to the light switch assembly next to the emergency brake release on the dashboard?

I like the safety aspect of having rear foglights and since apparently the switch assembly already can handle the hook-up, maybe I could do this.

I was just wondering if anybody had tried this and if anyone has any idea if one can buy connectors for the existing lightbulb sockets that are in the tailight assemblies.

Have you noticed how the taillight assembly has multiple connecting plug ?
This thing may already have the wire for the fog light as part of the bundle coming from the front of the car but not utilized from the plug to the empty socket....

Just a guess.
Take a look at this plus and investigate.
I haven't done it, but will later.
Not a priority now.

I was thinking the same thing; it would be nice to have the rear fog light feature working. To make it work, do I have to run a wire from the headlight switch or can it simply be done from the tail light connector?

Also, does anyone know a way to add the wire connector to the empty spaces where the bulb fits??

86' 300E tail lihgts have 5 bulbs, plug has 6 holes for pins, extra pin is for ground. I kind of doubt theres going to be an extra wire for the rear fogs, to bad though my switch also has the 2nd. detent and orange light in the center.
Chris C.

i've asked a benz engineer once why the rear foglamp is only on one side. The reason is that so it cannot be mistaken for a brake light. It is on the left for lefthand-drive cars so that it is in the direct line of sight of drivers following you in the same lane. also notice the location of the bumper-mounted rear foglamp of the benzwagon.

the reason for having those sockets on both lamp clusters is commonality of parts between lefthand- and righthand-drive cars - i assume that the righthand-drive cars use the right one as a foglamp.

anyway, my 1989 190e2.6 also has an empty, nonwired receptacle, and i would like to get hints on how to activate it, and what bulb to use, which fuse will be used, or if the fuse needs to be upgraded.

Here in canada, being seen well from the rear is of utmost importance, especially during low-visibility winter conditions.

and to me, an asymmetrically-lit rear looks very purposeful - and cool.

I played with the tail light bulb assembly on my 87 300 E, and the bulb carrier metal part pops out easily by gently spreading the plastic wings which hold the metal assembly. Once I find or make a metal contact for the plastic base, I plan to wire it to the existing brake light to give 4 brake lights instead of the existing 2. Any comments on the need to upgrade fuses, or the capacity of the wiring to handle the extra 12V32W bulb on each side? Would it be safer to use a 12V21W bulb in the new socket?
Maybe try one of the 12V 1 watt LED "bulbs" if current is a problem?